Vacuum electric arc furnace with lock chamber

ABSTRACT

A vacuum electric arc furnace for consumable electrodes, with a bottom section enclosing a crucible, a movable top section for accommodating the consumable electrodes, a lock chamber with a lock valve between bottom section and top section, and an annular splash protector. The annular splash protector is located concentric with the crucible axis and is movable vertically within the lock chamber. With the lock valve open, the protector is seated and with the lock valve closed it is flush with the top side of the valve and can be pressed against it. Towards the top, the annular splash protector turns into an apron which acts together with a fixed opposite apron in the lock chamber in telescope fashion throughout at least a major portion of the travel.

United States Patent Randa Oct. 14, 1975 [75] Inventor: Rudolf Randa, Grossauheim, Main,

Germany [73] Assignee: Leybold-Heraeus GmbH & Co. KG,

7 Cologne, Germany [22] Filed: Nov. 14, 1974 21 Appl. No.: 523,938

[30] Foreign Application Priority Data Nov. 15, 1973 Germany 2356996 [52,] US. Cl 13/31; 13/31 X [51] Int. Cl. F27D 7/06 [58] Field of Search 13/1, 9, 31, 14-17 [56] References Cited UNITED STATES PATENTS 1,610,819 12/1926 Steenstrup 13/31 X 2,976,339 3/1961 Gruber et a1. 13/31 lll/l 3,665,084 5/1972 Samietz et a]. 13/31 Primary ExamihrR. N. Envall, Jr. Attorney, Agent,'0r Firm.loseph F. Padlon ABSIRACT A vacuum electric arc furnace for consumable electrodes, with a bottom section enclosing a crucible, a movable top section for accommodating the consumable electrodes, a lock chamber with a lock valve between bottomsection and top section, and an annular splash protector. The annular splash protector is located concentric with the crucible axis and is movable vertically within the lock chamber. With the lock valve open, the protector is seated and with the lock valve closed it is flush with the top side of the valve and can be pressed against it. Towards the top, the annular splash protector turns into an apron which acts together with a fixed opposite apron in the lock chamber in telescope fashion throughout at least a major portion of the travel.

3 Claims, 3 Drawing Figures Z1 Ill/[l] VACUUM ELECTRIC ARC FURNACE WITH LOCK CHAMBER BACKGROUND OF THE INVENTION The present invention deals with a vacuum electric arc furnace for consumable electrodes with a bottom section enclosing a crucible, a movable top section for accommodating the consumable electrodes and a lock chamber betweenbottom section and top section. An annular-splash protector is provided for seating the lock valve.

As a result of the German patent DT-PS 1 I69 617, a vacuum electric arc furnace of the above described type belongs to the state of the art in which furnace top and bottom sections abut on both sides against a lock chamber in between, and are kept during the melting process at a distance corresponding to the height of the lock chamber. For example, after the end of the melting process, the furnace bottom section can be blocked by the lock valve,and the furnace top section can be lifted off so that the remolten metal can cool off in the absence of atmosphere. During the melting process, the edge of the crucible is protected by a horizontally swivelling annular splash protector against melt splashes. This annular splash protector which must be equipped with an additional drive cannot prevent melt splashes and dust from entering into the lock chamber during the overall operation of the electric arc furnace, thus endangering the drives for the lock valve and the annular splash protector contained therein. In addition, protection of the crucibleedge is possible only with limitations. After all, the lock valve rests only by its own weight against the crucible edges so that the sealing forces are relatively small. The eccentric drive also cannot support the sealing forces appreciably. Support for the sealing effect by the pressure of the atmosphere appears only gradually during flooding of the lock chamber. Frequently, initial leaks remain. The annular splash protector alsocannot be used to increase the sealing forces.

Through German patent DT-AS l 816 055 a solution has become known through which the press-on pressure of the lock valve is increased effectively and the inside of the lock chamber can be protected from dirt or damage. This is accomplished as follows: the furnace top section can be introduced into the lock chamber and can be selectively seated either on the lock valve or on the. crucible edge. However, this solution has the disadvantage that the relatively high volume and heavy furnace top section might be run into the lock chamber. The sealing against the lock chamber must be accomplished by an elastically deformable seal which is difficult to produce and in spite of everything has a certain susceptibility for difficulties in operation.

Therefore, the subject invention has the object of providing a furnace design where the furnace top section does not have to be introduced into the lock chamher, and where, nevertheless, a sufficient contact pressure of thevalve cover is assured, with complete protection of the lock chamber at the same time.

SUMMARY OF THE INVENTION The object of the present invention is achieved by the initially described vacuum electric arc furnace of the present invention. as follows: The annular splash protector is located concentric with the crucible axis and can be moved vertically inside the lock chamber. With the lock valve opened, it seats in its seat and with the lock valve closed it seats on its top side and presses against it. Towards the top, the annular splash protector turns into an apron which acts together with a fixed counter-apron in the lockchamber for at least a major part of the movement or stroke in telescope fashion.

Such a solution has the advantage that with the lock valve run in, the pressure of the annular splash protector against the lock valve provides sufficient sealing pressure. With laterally extended lock valve, the annular splash protector can be lowered onto the sealing surface, or the crucible edge, respectively and protects it against dirt accumulation. Through the telescope-like joint action of the two aprons which are concentric with the crucible axis and have the diameter of the crucible aperture, assurance is provided that no melt splashes and dust particles are existing-soiling or damaging the lock chamber. The expenditure for the vertical drive of the annular splash protector is conceivably low. 7

A particularly simple and reliable solution, in accordance with the subject invention, is characterized as follows. The annular splash protector is mounted swivell-like in a rocker arm located at the side of the crucible axis. This rocker arm reaches around the aprons in a hairpin-like fashion. The end or yoke of this rocker arm facing away from the pivots is connected to a drive. The annular splash protector is mounted" in the rocker arm rotatable about an axis which runs through the center of the lock valve parallel to the swivel axis of the rocker arm. The inherent or natural elasticity of the rocker arm, in conjunction with the pivoting, provides a cardanic suspension which guarantees a uniform seating, or pressure contact.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIGS. 1 3 are elevational sectional views and show a lengthwise section through a vacuum electric arc furnace in the area of the lock chamber in various operational phases, in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the vacuum furnace in the melt position. Part of the length of a consumable electrode 10 is surrounded by a movable furnace top section 1 1 consisting of a vacuum-tight reservoir with a connection to suitable vacuum pumps (not shown in the illustration). The furnace top section 1 lat its bottom end, has an annular flange 12 by means of which the'furnace top section is in indirect contact with a lock chamber 13 with an O-sealing ring in between. The external shape of the lock chamber 13 is that of a flat parallelepiped. Concentric with the consumable electrode 10, an aperture 15 is located in the upper boundary wall 14 of lock chamber 13. A fixed apron 16 is inserted in the aperture, with an O-sealing ring in between. This apron has the form of a hollow cylindrical stub and protrudes appreciably into the inside of lock chamber 13, surrounding the consumable electrode on all sides.

The lock chamber 13 has a lower boundary wall 17 which contains an aperture 18 concentric with the consumable electrode for inserting the consumable electrode. To the lower boundary wall 17, and to the aperture 18, there is connected, by means of an annular flange 19, an ingot mold 20 with an O-sealing ring between. In this mold, an ingot 21 to be produced is obtained by heat withdrawal and crystallization.

During the remelt process of consumable electrode 10 into ingot 21, a molten reservoir or pool 22 is located at the upper end of the ingot. This reservoir is fed by the dripping drops of the consumable electrode and its phase interface 23, because of continuous crystallization, progressively shifts upward. FIG. 1 shows the vacuum furnace shortly before the end of the remelt phase. The ingot mold 20 is surrounded by a cooling pot 24, leaving a hollow space 25. This hollow space contains the cooling medium. The cooling medium is guided by a cylindrical piece of sheet metal 26.

The upper surface of the lower boundary wall 17, in

an annular zone around the aperture 18, is made into a valve seat into which a lock valve 27 is seated. In the version according to FIG. 1, there seats in the valve seat (not further described) an annular splash protector 28 which turns in the upward direction into an apron 29. This apron likewise has the shape of a hollow cylindrical stub. It protrudes into the inside of the lock chamber 13 to such an extent that it extends over the fixed counter-apron 16 for all positions of the annular splash protector 28. The apron 29 and its counterpart 16 have diameters such that a mutual movement is possible without hindrance while providing sufficient shielding effect. It is evident that the two aprons 16 or 29, bound the space immediately adjacent to the consumable electrode 10. In this space there develops a great amount of heat with simultaneous appearance of melt spatters and dust formation. In this way, the interior of the lock chamber 13, located outside this space behind the aprons is reliably shielded and protected.

In the above-mentioned space in lock chamber 13 there is located, in addition to lock valve 27, a drive spindle 30 which enages the lock valve 27 through a spindle nut 31 and a transmission linkage 32. The drive spindle30 is fixed in bearing blocks 33 and 34, in the lock chamber. By actuating drive spindle 30, the lock valve 27 can be moved back and forth in the direction of the arrow shown parallel to the section plane. The lock valve rolls off on spring-supported rollers 35 on the associated rails.

Inside the lock chamber 13, on the side, far away from the crucible axis there is a bearing block 36 in which a hairpin shaped rocker arm 37 is supported by means of a swivel axis 38. The direction of the swivel axis 38 is at right angles to the drawing plane. The rocker arm 37 of which only the leg located behind the drawing plane is shown together with the associated bearing block, runs from bearing block 36 parallel to the section plane through the lock chamber 13 around apron 29 and again back to the second bearing block in which is located symmetrically relative to bearing block 36 (in relation to the section plane). At the yoke 37a of the rocker arm, there is an extension 39 with an inserted spindle nut 40 which engages with a vertical drive spindle 41. Drive spindle 41 is located in the upper or lower boundary wall of lock chamber 13.

When actuating drive spindle 41, spindle nut 40 and with it rocker arm 37, depending on the direction of rotation, moves upwards or downwards and takes along the annular splash protector 28 and apron 29 which are connected to rocker arm 37 by way of swivel axis 42. Swivel axis 42 runs parallel to swivel axis 38. The annular splash protector 28 and apron 29 can execute small swivel motions relative to rocker arm 37. Spindle nut 40 and drive spindle 41 constitute the so-called drive 43 for rocker arm 37. The latter, because of its dimensioning, permits a certain amount of torsion so that the annular splash protector 28 can be made to contact the valve seat along its entire surface.

FIG. 2 shows the vacuum furnace in a position immediately after termination of the remelt process. The remainder of the consumable electrode 10 has already been pulled upward into the furnace top section 11 and is, therefore, not visible on the drawing. By actuating drive 43, the spindle nut 40, the rocker arm 37 and the annular splash protector 28 with the apron 29 were lifted to such an extent, that the resulting space between the valve seat and the lower boundary surface of the annular splash protector 28 is sufficient for introducing the lock valve 27. Apron 16 and 28 slide over each other in telescope fashion. The lock valve is just at the start of its motion in the direction of the arrow drawn. This is effected by actuating the drive spindle 30.

FIG. 3 shows the vacuum furnace in a position where the lock valve 27 has reached the intended position above aperture 18. The rotation of drive spindle 30 has come to rest, whereupon rocker arm 37 was moved downward under the influence of drive 43. The annular splash protector 28 seated on the top side of lock valve 27. By suitable further rotation of drive 43, the annular splash protector 28 can be further pressed against the lock valve 17 by means of rocker arm 37. Lock valve 17 is pressed against the associated valve seat with great force, so that the sealing effect is present already at a point in time when an atmospheric pressure differential on both sides of the lock valve 27 cannot yet assist the sealing effect. Furnace top section 11 (not shown in FIG. 3) has already been removed and can be used in conjunction with another ingot mold and a lock chamber for another remelt process, while the molten metal contained in the mold 20, or the ingot 21, can cool off in the absence of atmosphere. To remove ingot 21, mold 20 is pulled downward. Subsequently, it or another mold can be brought to aperture 18 whereupon rocker arm 37 with annular splash protector 28 is lifted up and lock valve 27 is returned to the position shown in FIG. 1. After attaching the furnace top section 11 equipped with a new consumable electrode 10, the furnace is ready for another remelt process. During remelting, another batch of molten metal, or another ingot, can cool off in an adjacent mold 20 analogous with the above explanation, in the absence of atmosphere.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

l. A vacuum electric arc furnace for consumable electrodes comprising, in combination, a crucible; a bottom section enclosing said crucible; a movable top section for receiving said consumable electrodes; a lock chamber between said bottom section and said top section and having a lock valve; an annular splash protector concentric with the crucible axis and movable vertically with said lock chamber, said splash protector being seated on said lock valve when said lock valve is closed, said splash protector being flush with the top side of said valve and being pressable thereto, said splash protector turning into an apron towards the top, said lock chamber having a fixed opposite apron cooperating with the apron of the splash protector telescopically throughout at least a major portion of the travel.

2. The furnace as defined in claim 1 including a rocker am on the side of the crucible axis, said splash protector being mounted swivel-like in said rocker arm, said rocker arm reaching around said aprons in hairpin like shape; and drive means connected to the end of said rocker arm facing away from the pivot of said rocker armf 3. The furnace as defined in claim 1 wherein the pivot axis of said splash protector is parallel to the pivot axis of said rocker arm and passes through the crucible axis. 

1. A vacuum electric arc furnace for consumable electrodes comprising, in combination, a crucible; a bottom section enclosing said crucible; a movable top section for receiving said consumable electrodes; a lock chamber between said bottom section and said top section and having a lock valve; an annular splash protector concentric with the crucible axis and movable vertically with said lock chamber, said splash protector being seated on said lock valve when said lock valve is closed, said splash protector being flush with the top side of said valve and being pressable thereto, said splash protector turning into an apron towards the top, said lock chamber having a fixed opposite apron cooperating with the apron of the splash protector telescopically throughout at least a major portion of the travel.
 2. The furnace as defined in claim 1 including a rocker arm on the side of the crucible axis, said splash protector being mounted swivel-like in said rocker arm, said rocker arm reaching around said aprons in hairpin-like shape; and drive means connected to the end of said rocker arm facing away from the pivot of said rocker arm.
 3. The furnace as defined in claim 1 wherein the pivot axis of said splash protector is parallel to the pivot axis of said rocker arm and passes through the crucible axis. 